The densification of biomass involves the grinding, separating and compacting of biomass into small pellets or cubes. This technology is already being used to densify biomass into pellets for use in stoves that have the ability to create electricity and heat, also known as combined heat and power (CHP). The densification of biomass can also be applied towards the biochemical conversion of biomass into fuels, chemicals and electrical energy through the use of related gasification technologies, of which there are several to choose from. Some gasification technologies include Pyrolysis, Fischer-Tropsch and Mixed Alcohol production. Densification may be the favorable form to produce biofuels through gasification. For example, one type of gasification technology called pyrolysis can convert biomass into several different chemical fractions that can be separated and used towards electricity, chemicals or fuels. In one pyrolysis study, three types of chemical fractions were produced from cellulosic materials, those being 1)synthesis gas components, 2) Light condensables which consist of acids, ketones and alcohols and 3) tar like fraction that consists of furan compounds, phenolics and other chemicals [ 1. E. Soltes 1988 ]. Densification of biomass could be applied towards the simultaneous production of electricity and other chemicals such as mixed alcohols and hydrocarbons from synthesis gas, which are emerging production methods. Sythesis gas produced from gasification can also be converted into Naptha or diesel fractions through the use of Fischer-Tropsch technology. Thermochemical processing of biomass into fuels should also allow the production of cellulosic ethanol to reach around $1.00 per gallon. In fact, the use of thermochemical based biorefineries may be needed in order to produce ethanol at very high quantities as well as becoming energy efficient by producing heat and power for related refining processes.
If large enough biorefineries are built such as those that can process 100 + Mega Million (MM) Gallons of ethanol per year, they should be able to make enough electrical power that can be put back into the electric grid. There are various other benefits to densifying biomass. It is easier to transport and store biomass when it is densified, this helps to deliver and transport biomass to thermochemical processing plants effectively. This is due to the fact that biomass in its loose, original form is irregular shaped or spatially scattered which makes it difficult to collect and store [ 2. J. Singh et al 2010 ]. In addition, densification reduces moisture content and reduces material waste in handling. However, the cost of densification into pellets or other forms makes it impractable currently for its use in biorefineries. For example, a densification plant that uses corn stover may be able to produce pellets at around $60 per ton but large biorefineries such as those operated by the government, may be able to purchase corn stover at a cost of only $35 per ton [ 3. Aden 2007 DOE ]. The ideal crop residues to use for densification may be corn stover as well as straw residues like wheat, barley, oat and canola and energy crops such as switchgrass [ 4. S. Mani et al 2006 ]. It is however, more difficult to use lignocellulosic based residues due to the tar material that must be cleaned as it is gasified. The conversion of municipal waste into electricity, fuels and chemicals may also be another source of potential fuels from refuse derived fuel (RDF) that must also be densified in order to be processed thermochemically. Municipal waste processing plants are already being built that can convert around 2000 tons of RDF per day into mixed alcohols using thermochemical gasification.
REFERENCES
1. "Pyrolysis Oils from Biomass : Producing, Analyzing & Upgrading" - E.J. Soltes, T.A. Milne - ACS 1988
2. "A Mathematical Model for Transporting the Biomass to Biomass Based Power Plant", by J. Singh, BS Panesar, SK Sharma, Biomass and Bioenergy - Vol 34 pgs 483-488 [2010]
3. "Biomass & Biofuels : Technology & Economic Overview" NREL - by Andy Aden [2007]
4. "Economics of Producing Fuel Pellets from Biomass" by S.Mani, S.Sokhensanj, X.Bi & A.Turhollow, Applied Energy in Agriculture - Vol 22 No 3 pgs 421-426 [2006]
KEYWORDS: Densification of Biomass, Mixed Alcohol Production, Pyrolysis, Fischer Tropsch Synthesis, Refuse Derived Fuel, Thermochemical Biorefineries, Cellulosic Ethanol, Crop Residual Waste, Combined Heat and Power, Furfurals, Phenolics, Synthesis Gas
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